Am I legally allowed to beat up this dude?

Why would you let this little piece of ignorant puke get you so angry you risk going to jail for a felony? That will be on your record and will have a negative effect on you. Is he worth it? Some half brained idiot dickless little punk? Avoid him and if he bothers you again yell at him but whatever you do, do NOT TOUCH him. You can also tell him if he touches you one more time that is assault and then you can report HIM and get HIM in trouble.